1. Field of the Invention
This invention relates to the containment of environmentally hazardous materials, and in particular, to a system for detecting, locating, and containing a leak from an impoundment. The system consists of a mobile sensor system that is used in combination with a system of leak detection modules installed beneath an impoundment. The combination permits detecting, locating and containing leaks from an impoundment, as well as permitting leak repair. The invention is directed to both an apparatus for detecting and repairing leaks as well as to a method of doing the same.
2. Description of the Prior Art
Storage and disposal of hazardous waste is a matter of significant public concern given the health and safety risks which can result from a leak. Presently, such storage is often accomplished in various types of impoundments which may include landfills, surface tanks, underground tanks as well as other structures designed to contain the hazardous materials and to prevent leakage or migration of the hazardous materials out into the environment.
To alleviate the risk of environmental contamination, government regulations require the installation (in many situations) of one or more synthetic liners, known as secondary containment systems, below landfills and many other impoundments of hazardous or potentially hazardous materials. The liners typically are large sheets of flexible, polymeric material, such as high density polyethylene, and are intended to resist degradation caused by the environment and contact with caustic hazardous waste. During construction of the impoundment, individual sheets of the liner material are seamed together at the construction site to form a continuous liner which extends below and completely encompasses the bottom of the impoundment. Where more than one liner is used, a layer of clay or some other material having a low permeability is often placed between the liners.
Although the liners are intended to be impermeable, in fact many will eventually develop leaks. Recognizing the difficulty of having a liner or liner system that is completely free of leaks, some leakage is expected and permitted. In fact, government regulations permit some defined leakage per acre per day through a liner. Government regulations also require that the liners or secondary containment system be augmented by a number of monitoring wells at locations surrounding and adjacent to the impoundment. The purpose of the monitoring wells is to allow for the periodic testing of groundwater below the impoundment. The detection of hazardous material in the groundwater indicates a failure of the secondary containment system.
There are, however, some serious shortcomings associated with the use of synthetic liners and monitoring wells for the safe storage and disposal of hazardous waste. First, as noted above, synthetic liners unfortunately have a tendency to develop leaks over time. The leaks can be caused by a number of factors such as punctures, split seams, and differential settling of the underlying soil. Once a leak occurs, there is nothing to prevent the hazardous material from escaping the impoundment and contaminating nearby soil, surface water, and groundwater. Second, when a leak is first discovered through the detection of hazardous material in a groundwater sample taken from a monitoring well, significant damage to the environment will have already been inflicted. The hazardous waste will have already contaminated groundwater, an important source of public drinking water. Finally, the detection of hazardous waste in samples taken from the monitoring wells only reveals the existence of a leak, it provides no useful information as to the location and severity of the leak. Consequently, to correct the problem, it is necessary to remove the entire impoundment and completely replace all synthetic liners at an enormous financial cost. Such remedial measures also pose an increased danger to public health and safety because of the additional contact with the relocated hazardous waste.
The present inventor has previously proposed solutions for some of these problems as shown in Hampton et al., U.S. Pat. Nos. 5,460,032 and 5,583,283; The Hampton et al. patents describe an apparatus for the detection, location, and containment of leaks from impoundments which contain potentially hazardous waste. The apparatus consists of a modular structure designed to be installed below the impoundment, thereby forming a collection grid. The structure is installed either below the synthetic liner as an impoundment's secondary containment system or below the lowest layer of an impoundment which does not employ a liner. The apparatus comprises a plurality of leak detection modules for collecting and localizing fluid escaping from a leak in the above impoundment, and each of the modules is provided with a conduit connected to a tunnel extending beneath the structure. Such apparatus provides that leaking fluid will be directed from the module nearest the leak via the connected conduit to an underlying access location. By providing sensors in the underlying access location, leaking fluid may be detected and the severity of the leak ascertained. Additionally, because each conduit is connected to a specific leak detection module, the position of the leak can be localized to the vicinity of that module. Furthermore, because fluid which leaks through the liner is collected by the conduit system, any fluid which has leaked may be pumped out, collected or otherwise safely disposed.
Although the above-described inventions offer substantial capabilities over the previously available technologies for detection and localization of leaks, as well as for collection of any potentially hazardous fluid which may escape due to a leak, economic considerations demand that any impoundment system be as affordable as possible. Additionally, considerations in ease of fabrication, installation, and maintenance mandate that the system lend itself to conventional construction methods and tools. Finally, different waste compounds pose varying degrees of environmental risk, mandating that varying degrees of security be available in the impoundment system, each with a cost corresponding to the degree of security required.
Thus, there remains a need for an impoundment leak detection and containment system which is highly effective yet affordable, easy to fabricate and install using conventional tools and construction techniques, and which offers varying levels of protection which may be tailored to the various types of materials to be impounded.